Register vendor JS/CSS only on pages that require them?

How are the UI Elements included on the page? If you use a shortcode, you can enqueue the js part (wp_enqueue_script) within the shortcode function. Your JS will then be enqueued in the footer. The CSS would have to be enqueued of course in the header, so you have to enqueue it in the wp_enqueue_scripts action. If you only need it on the pages that have the shortcode, you can do something like this in your wp_enqueue_scripts action function:

add_action('wp_enqueue_scripts','my_awesome_function');

function my_awesome_function(){
  if(is_singular()){
    global $post;
    if(has_shortcode($post->post_content,'my_awesome_shortcode')){
       wp_enqueue_style('my-awesome-style');
    }
  }
}

Happy Coding!